Track circuit for railroads



Nov. 8, 1938.

' TRACK CIRCUIT FOR RAILROADS J. E. WILLING 2,135,548

Filed June 14, 1934 h, ATTORNEY Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE Joseph E. Willing, Rochester, N. Y.. assignor to General Railway Signal Company, Rochester,

Application June 14, 1934, Serial No. 730,646

12 Claims.

This invention relates in general to track circuits such asused in railway signalling practice and has more particular reference to means for increasing the efliciency ofshunting and discriminating between a shunt provided by a train in the track section and a shunt due to ballast conditions.

In railway operation it is quite essential that the track relay connected across the track section at one end of a signalling block be sufiiciently energized. when the block is unoccupied to pick up and hold up with certainty. It is likewise essential that the occupancy of the track section willeffectively shunt the relay so that it will be positively released. For examplain the usual track circuit if the normal holding current is too high, shunting may not be effective to drop the relay and if the normal holding current is so lowthat shunting will bemore positive, then it is possible that at times the holding current may be insuflicient to hold the relay in its picked up 7 position when the track section is not occupied.-'

Taking the above into consideration. it will be seenthat the usual variation in ballast resistance encountered in practice, due primarily to changes in weatherconditions, -may operate to interfere with the proper operation of the track relay unless some means is provided for discriminating between changesdue to ballast leakage and track occupancy.

As the ballast resistance increases, the leakage current between the rails decreases so that the voltage across the terminals of the track relayconnected to the track circuit increases.

Conversely as the ballast resistance decreases,-

ballast leakage increases and the terminal voltage'at the relay terminals decreases. vision is made for regulating the current flow through the relay this current will vary over a considerable range and'possibly cover a range at times which-will prevent proper response of the relayunder occupied and unoccupied conditions whichdiscriminates between aslow change in Unless pro-- track shunt due to track ballast and a rapid change in track shunt due to train occupancy.

Further objects, purposes and characteristic features of the invention will appear as the description, progresses, reference being made to the accompanying drawing which shows by way of example one form that the invention may assume.

The single figure diagrammatically illustrates one form of the present invention applied to a single stretch of track.

Apparatus-A section of railway track including rails I is shown separated from the adjacent track sections by insulated joints 2. A track battery B and a limiting resistance D are shown connected to the track rails at the right hand end of the illustrated track section. The primary winding of a transformer TR is included in series with the circuit extending from the lower track rail to the track battery, the secondary of this transformer being connected to a relay G which is for the purpose of including and excluding resistance Hfrom the track circuit for locking relay A, as will be later described.

Relay A is normally energized and when it drops to close its normally open back contact, resistance 0 is removed from the track circuit. The limiting resistor D is adjustable in order to regulate the current flow from battery B to the track rails for the most efficient operation.

Track relay T is shown connected across the track rails at the left end of the illustrated track section. As typical of the control exercised by the track relay, a semaphore signal SG is illustrated and it will be understood that any suitable type of signal may be used, of which SG is merely a typical example.

Normal conditi0ns.With the circuit in its normal condition as illustrated in the figure, track relay T is normally picked up over a circuit extending from the terminal of battery B, primary winding of transformer TR, lower track rail, winding of relay T, upper track rail, resistances D and C in series to the terminal of battery B. The current flow in this circuit maintains relay T in its picked up condition. A circuit inshunt of relay T and the primary winding of transformer TR includes the winding of relay A and resistance H in series. Under normal or dry ballast conditions current through this shunt circuit is effective to maintain relay A in its picked up position. This circuit may be traced from the terminal of battery B, resistance H, winding of relay A, resistances D and C in series to the terminal of battery B.

Ballast changes-A decrease in resistance between the rails of the track due to the ballast conditions changing (by increasing the shunt path between these rails) tends to reduce the current flow through the shunt path including relay A because of the increased potential drop across the circuit including the primary winding of transformer TR and relay T, which drop reduces the potential drop across the'circuit including relay A and resistance H.

Consequently when the leakage current due .to

an impaired ballast condition increases'to a predetermined value, relay A is sufficiently shunted to drop its armature. The closure of back contact 3 of relay A short circuits resistance C which removes this resistance from the circuit leading to the track rails so that more current flows through the track rails and relay T in series. The effect is, therefore, to increase the current flow through relay T when the ballast shunt reaches a value which causes relay A to drop. As ballast conditions improve, a point will be reached where the ballast resistance is increased to such a value that the effective shunting effect of relay A is diminished to the point which will allow relay A to pick 7 up and again insert resistance C in the track circuit for placing the circuits in the conditions illustrated in the figure.

Track oceupancy.-Assuming that ballast conditions are such that relay A is picked up, the entrance of a train into the illustrated track section causes a sudden increase of current through the primary winding of transformer TR due to the sudden shunting of relay T. This sudden rush of current through the primary winding of the transformer sets up a potential across the secondary winding, including the winding of the mag-stick polar relay G, in such a direction that relay G operates its polar contact 4 to the left. It will be understood that although this induced current in the secondary winding of the transformer is only momentary it is of sufficient duration to operate the contact of relay G.

Contact 4 actuated to its left hand dotted position short circuits resistance H which decreases the resistance of the shunt path across the track circuit by removing this resistance. This decrease in the shunt resistance has the effect of increasing the sensitivity of relay T to the train shunt.

When'the train leaves the illustrated track section, the sudden removal of the shunt across track relay T causes 'a sudden decrease in current through the primary winding of transformer TR which induces a potential in its secondary winding opposite to that previously described, which is eifective to operate contact 4 of relay G to" the right. This removes the short circuit from resistor H which places the circuits in the condition shown in the drawing.

Since relay G is of the polar type and since it is energized by an impulse of current quickly generated in the secondary winding of the transformer, it will be understood that the response of' its contact 4 is substantially faster than the re.- sponseof contact 5 of relay T, both when the track section becomes occupied and when'it becomes unoccupied. I

From the above description it will be noted that relay A acts as a potential relay which cuts out resistance C when track ballast resistance is low and cuts resistance C back in the circuit when the ballast resistance increases to a predetermined cut-over point, which is effective to main tain the circuit in condition for greatest train shunting efficiency.

Itwill also be noted that relay G, transformer TR. and resistance l-I provide the lockout of relay A on instantaneous shunt and that these ele.

merits remove the lookout of relay A on quick removal of the shunt, thus making the locking out and the removal of the locking out functions responsive to train shunt but not responsive to changes in ballast resistance caused by Weather conditions. It will be understood that the lockout of relay A due to track occupancy is the re-. moval of resistance H by the operation of relay G to give relay A morecurrent so that it will remain in its picked up position.

Under the worst ballast conditions, when relay Contact 5 of relay T may be used to control thesignal' circuits of signal SG or for any other purpose required by the usual practice in connection with track relay circuits.

Summary-With the track conditions normal (high resistance shunt due to a dry track), the track relay T is maintained energized as long as the track is unoccupied by means of current flowing from battery B through resistors C and D and the primary winding of the transformer. in series. 'When a train enters the track under this condition. the low resistance shunt placed across the track rails causes an increase of current flow through resistors C and D and the primary winding of transformer TR. Due 'to the shunting effect of the train a reduction in current flow takes place in track relay T, regulator relay Aand resistor H; r y a This sudden increase in current through the primary of the transformer operates contact 4 of relay G to the left which removes resistor H from the circuit by short circuiting it. This causes a further increase in current flow through resistors C and D and a" further reduction in current flow through relay T (because of the increased shunt conductance) as well as an increase in current flow through the winding of relay A. All of this is eifective to accomplish the release of relay T.

Whenthe train leaves the track section under this condition the current flow through resistances C and D is suddenly reduced which is accomthrough the primary of transformerTR as well 7 as an increase in current flow through the winding of relay A and through the winding of relay 'T. This sudden reduction in current flow through the transformer winding is effective to operate contact 4 of relay G to the right which inserts resistance H in the circuit for further reducing the current flow through resistances C and D and the winding of relay A, while the current flow through relay T is further increased' When the rails of the track are slowly shunted due to the ballast conductance changing in response to wet weather conditions, the current through resistances C and D and the primary windingof transformer TB is slowly increased. This condition effects a reduction in current flow through relays T and A and resistorH until 7 5 a point is reached where'relay A drops its-back contact to shortcircuit resistance C. This re-' moves resistance C from the circuit, effecting a slight sudden increase in current through resistor Dand the primary winding of transformer TR" aswell as through thewindings of relays T and A and the resistor H.- This'slight increase in current is not sufficient to cause the operation of relay G.

When a train enters the track section under this condition, a'sudden and large increase of current flow takes place through resistor D and theprimarywinding of transformer TR While a reduction in current flow takesplace through the winding of relays T and A and resistor H. This sudden increase in current through the transformer operates contact 4 of relay G to the left which short circuits resistor H and removes-it from the circuit, thereby causing a further increase in current flow through relay A as well as a reduction in current flow through the primary winding of transformer TR and the winding of relay T.

When the train leaves the track section, a reduction'in current flow takes place through resistor D and the primary winding of transformer TR as well as an increase in current flow through the windings'of relays A and T. This sudden reduction in current flow through the transformer winding operates contact 4 of relay G- to the right/which inserts resistance H in the circuit for further reducing the current flow through resistor D and relay A and for increasing the current flow through the primary winding of transformer TR and the winding of track relay T.

When the track is occupied, an increase in the shunt across the rails due to a wet track condi-- tion has the effect of applying an additional shunt to track relay T and since this relay is already shunted down by the train this condition has no noticeableefiect. Relay A will not drop under this condition because resistance H is shunted out and when the train leaves the track section resistance H is cut into the circuit which may or may not drop relay A, both of which applies more current to track relay T for causing it to pick up.

The drying out of the track ballast during track occupancy has no effect on relays T or A because relay T is effectively shunted by the train and since this shunt is not noticeably changed by the drying out of the ballast, relay A does not change its position. When the train leaves the track section under this condition resistance H is 'cut into circuit which supplies relay A with more current so that it will receive suflicient current to pick up if the track has dried out to the cut-over point.

It will be clear from the above description that this invention provides means whereby there is a positive discrimination between the track circuit conditions due to track occupancy and due to ballast leakage and that changes in ballast leakage condition the circuits for more efficient shunting of the track relay by the train.

The above rather specific description of one form of the present invention has been given solely by way of illustration and is not intended in any manner whatsoever in a limiting sense. It will be obvious that the general principles herein disclosed may be embodied in many other organizationswidely difierent from that illus- What I claim is:--

1. An automatic voltage regulator for a track circuit comprising; a source of current connected'to the rails of a track; a resistor in the con-. nection between said source and said rails; a track relay connected across the rails of said track; a second relay connected in shunt of said track circuit; said second relay being adapted to effectively exclude said resistor from said connection when the voltage of said track circuit falls below a predetermined value and to effectively include said resistor in said connection when the voltage of the track circuit increases above a predetermined value; and auxiliary means for effectively including a second resistor in and excluding it from said shunt.

2. An automatic voltage regulator for a track circuit comprising; a source of current connected to the rails of a track; a resistor in the connection between said source and said rails; a track relay connected across the rails of said track; a second relay connected in shunt of said track circuit, said second relay being adapted to effectively exclude said resistor from said connection when the voltage of said track circuit falls below a predetermined value and toeffectively include said resistor in said connection when the voltage of the track circuit increases above a predetermined value; and auxiliary means for effectively including a second resistor in and excluding it from said shunt, said auxiliary means responding only to a rapid change of current flow in said track circuit caused by the sudden application or removal of a vehicle shunt.

3. An automatic voltage regulator for track circuits, comprising, in combination with the track circuit and a source of current supply for said track circuit having an adjustable resistance in series therein, a second resistance connected in series with said adjustable resistance and the source of current supply, contact points electrically connected between the two resistances and the current supply, a relay and a third resistance in series included in multiple with said resistances and said source, means controlled by said relay for causing said contact points to effectively include and exclude said second resistance from said circuit, said relay being responsive to the slow increase and the slow decrease of the shunt resistance across said track circuit to control said contacts. and means responsive to the quick application and the quick removal of a shunt across said track circuit for effectively excluding and including said third resistance whereby the operating and release voltage values of the circuit of said relay are varied.

4. In combination, a section of railway track, a source of current connected across the rails of said section, a first relay receiving energy from the rails of said section and responsive to the steady value of current with which it is supplied, a second relay, means also receiving energy from the rails of said section for energizing said second relay when the value of the current received by said means is changed due to the entrance of a train into said section, said means being incapable of responding to the steady value of such current, and means controlled by said second relay for decreasing the energization of said first relay.

5. A track circuit for a section of railway track including a source of unidirectional current; a transformer having its primary winding included directly in said track circuit; a polarity responsive device included directly in series in the secondary winding of said transformer; a track relay energized to an extent. depending upon the value of current flowing .in said track circuit; and means including a contact of said polarity responsive device actuated, in response to a sudden increase in the current in the primary winding of said transformer, to a position to decrease the degree of energization of said track relay; whereby said track relay is also controlled in accordance with the rate of change in a particular direction of current flow in said track circuit.

6. A track circuit for railroads comprising, a section of railway track, a source of unidirectional current connected across the track rails at one end of said section, a track relayreceiving energy from the track rails at the other end of said section, a transformer having its primary winding included in said track circuit; and an auxiliary relay energized only by-current induced in the secondary winding of said transformer, and operated in response to the relatively quick change of current in the track circuit caused by the entrance of a train into said section for decreasing the current through said track relay to release its armature.

7. A track circuit for railroads comprising, a uni-directional source of current and a track relay in series, a transformerhaving itsprimary winding included in, said track circuit, and an auxiliary relay energized only by current induced in the secondary winding of said transformer and causing operation of a contact to a particular position only when current in one direction is induced in said secondary winding by the relatively quick change in the current in said track circuit 9-. In combination, a section of railway track, a source of current connected across the rails of said sections, a relay receiving energy from said rails, a device responsive to the entry of a train into said section, and means including a contact controlled by said device for shunting the rails of said section when a train enters the section.

10. In combination, a section of railway track, a source of current connected across the rails of said section, a track relay receiving energy from said rails, a device receiving energy from said source and responsive to the entry of 'a train insaid section, and a shunting path for the rails of said section controlled bysaid device.

11. In a track circuit; in combination with an insulated stretch of track; a source of current connected acrossone end and a track relay connected across the other end of said track; electromagnetic regulating means connected to the track rails at said one end for automatically increasing the current supplied to said track when the voltage across saidone end due to slow variations in the inter-rail resistance falls below a particular value; and impulse actuated means responsive to.

a rapid decrease in said inter-rail resistance for causing a decrease in the current supplied to said 1 track below that existing immediately after such rapid decrease in inter-rail resistance occurred, said impulse actuated means comprising a polar relay operated to one position in response to a rapid increase ininter-rail resistance and to another position in=response to a rapid decrease in inter-rail resistance. 7 v 12. In a track circuit, a track relay, track rails, a regulator relay arranged to automatically increase the energizing current through said track rails and track relay when the potential across the track rails adjacent said regulator relay due to weather conditions on said track circuit falls below a particular value, and an impulse actuated locking means inductively coupled with said track circuit so as to be distinctively responsive to the shunting of said track rails by a train for when assuming one condition preventing a change in position of said regulator relay. V

JOSEPH E. WILLING. 

